A wireless communication system has been widely developed to provide various kinds of communication services such as voice and data. Generally, the wireless communication system is a multiple access system that can support communication with multiple users by sharing available system resources (bandwidth, transmission power, etc.). Examples of the multiple access system include a code division multiple access (CDMA) system, a frequency division multiple access (FDMA) system, a time division multiple access (TDMA) system, an orthogonal frequency division multiple access (OFDMA) system, and a single carrier frequency division multiple access (SC-FDMA) system.
In recent years, distributed antenna systems (DASs) have gained interests because of its ability to extend the cell coverage and increase the system capacity. Unlike conventional centralized antenna systems (CASs) where all antennas are co-located at the cell center, distributed antenna (DA) ports in the DAS are separated geographically. Thus, the DAS can reduce the access distance along with the transmit power and co-channel interference, which results in improved cell-edge performance.
For conventional closed-loop CAS where channel state information (CSI) at the transmitter is utilized, optimization on power allocation and a precoding design have been heavily conducted. However, only a few papers have studied the closed-loop DAS. In DAS, an achievable capacity expression was derived with analytical closed forms for spatial multiplexing transmission. Also, conventional art (e.g., MIMO channel capacity for the distributed antenna systems) studied the capacity of DAS with the random antenna layout in a single-cell and proposed a sub-optimal power allocation scheme. In addition, a sectorized distributed antenna structure was introduced and a power adjusted beam switching scheme was proposed.
In practical limited feedback systems, each user first quantizes instantaneous channel realizations and feeds back the index of the quantized channel to the transmitter by using a codebook. For multiple-input multiple-output (MIMO) CAS, a codebook design problem was first solved by utilizing a distribution of the optimal beamforming vector in independent and identically distributed (i.i.d.) Rayleigh fading matrix channels. Also, several papers studied feedback bit allocation schemes for the conventional CAS with limited feedback. The article (e.g., L. Dai, S. Zhou, and Y. Yao, “Capacity Analysis in CDMA distributed antenna systems”) provided various issues of DAS with limited feedback focusing on the challenges in codebook designs and proposed a suboptimal codebook design suitable for the DAS. However, the methods and apparatus of the conventional studies waste feedback information and radio resources because these methods and apparatus consider so many factors of realization channels.